It is attempted to apply a submarine cable system as an observation system for earthquake, resources, and the like by mounting various sensors suitable for purposes and intended uses in submarine equipment constituting the submarine cable system. In the submarine cable system functioning as such an observation system, physical phenomena having arisen on seabed, such as a vibration, a variation of water pressure, a variation of magnetism, and the like, are measured by sensors incorporated in equipment placed on the seabed, such as a submarine repeater or the like. The submarine cable system functioning as the observation system is disclosed in, for example, patent literature (PTL) 1 and PTL 2.
Here, for the submarine cable system, there are lots of cases where the total length of the distance including a terminal device constructed on land and submarine equipment constructed on seabed is longer than or equal to 1000 km. In the case where the total length is longer than or equal to 1000 km, it is difficult to supply a constant voltage from a power supply device on land to the undersea submarine equipment. Thus, in the submarine cable system in PTL 1, a constant-current power supply scheme is employed. Here, the constant-current power supply scheme is a scheme for supplying a constant current, as a power source, to the undersea submarine equipment from the power supply device on land via a power cable.
A block configuration diagram of submarine equipment disclosed in PTL 1 is illustrated in FIG. 5. In FIG. 5, submarine equipment 900 in PTL 1 includes a switching circuit 910, a transformer 920, a rectifier circuit 930, a Zener diode 940, a heat sink 950, and an observation equipment circuit 960.
The switching circuit 910 performs switching of a constant current supplied from a power supply device on land, and generates a rectangular wave voltage. The transformer 920 converts the rectangular wave voltage, which results from the switching by the switching circuit 910, into a desired voltage, and supplies the voltage to the rectifier circuit 930. The rectifier circuit 930 rectifies and converts the supplied rectangular wave voltage of a desired magnitude into a direct-current voltage, and supplies a constant current to the observation equipment circuit 960. The observation equipment circuit 960 is subjected to power-source on/off control and various kinds of operation settings by remote control from land, and is driven by the constant current supplied from the rectifier circuit 930.
Meanwhile, the Zener diode 940 is disposed in parallel to the observation equipment circuit 960 to absorb a variation portion of power consumption in the observation equipment circuit 960, and radiates the absorbed power as heat into seawater through the heat sink 950.
The variation portion of the power consumption of the observation equipment circuit 960 is absorbed by the Zener diode 940, and thus, the sum of the power consumption of the observation equipment circuit 960 and the power consumption of the Zener diode 940 always becomes constant. The sum of the power consumption of the observation equipment circuit 960 and the power consumption of the Zener diode 940 is equivalent to an output current of the rectifier circuit 930, and thus, the output current of the rectifier circuit 930 takes a constant value. Accordingly, the submarine equipment 900 in PTL 1 operates based on the constant current.